taken at varying depths, the apparatus
designed by v. Esmarch (Fig. 203) is employed. In this the sterilised
bottle is enclosed in a weighted metal cage which can be lowered, by
means of a graduated line, until the required depth is reached. At this
point the bottle is opened by a thin wire cord attached to the stopper;
when the bottle is full (as judged by the air bubbles ceasing to rise)
the pull on the cord is released and the tension of the spiral spring
above the stopper again forces it into the neck of the bottle. When the
apparatus is taken out of the water, the small bottles are filled from
it, and packed in the ice-box mentioned below.

An inexpensive substitute for Esmarch's bottle can be made in the
laboratory thus:

Select a wide-mouthed glass stoppered bottle of about 500 c.c. capacity
(about 20 cm. high and 8 cm. in diameter).

Remove the glass stopper and insert a rubber cork with two perforations
in its place.

Through one perforation pass a piece of glass tubing about 5 cm. long
and through the other a piece 22 cm. long, reaching to near the bottom
of the bottle, each tube projecting about 2.5 cm. above the rubber
stopper. Plug the open ends of the tubes with cotton wool. Secure the
stopper in place with thin copper wire.

[Illustration: FIG. 204.--Thresh's deep water sampling bottle.]

Sterilise the fitted bottle in the autoclave. Remove the cotton wool
plugs and connect the projecting tubes by a piece of loosely fitting
stout rubber pressure tubing about 5 cm. long, previously sterilised by
boiling.

Take a piece of stout rubber cord about 33 cm. long, and of 10 mm.
diameter (such as is used for door springs) thread a steel split ring
upon it and secure the free ends tightly to the neck of the bottle by
cord or catgut.

Attach the cord used for lowering the bottle into the water to the split
ring on the rubber suspender. The best material for this purpose is
cotton insulated electric wire knotted at every metre.

Connect the split ring also with the short piece of rubber tubing
uniting the two glass tubes by a piece of catgut (or thin copper wire)
of such length that when the bottle is suspended there is no pull upon
the rubber tube, but which, however, will be easily jerked off when a
sharp pull is given to the suspending cord.

Now wind heavy lead tubing about 1 cm. diameter around the upper part of
the bottle, starting at the neck just above the shoulder. This ensures
the sinking of t